Conjunctivitis
By Dr. Karen Burgess

What is conjunctival tissue?
The conjunctiva is the pink fleshy tissue that covers the eye and tissue surrounding it.  In a cat or dog with healthy eyes this conjunctiva should not be easily seen.  In cases of conjunctivitis where the conjunctiva is inflamed owners will often notice angry red tissue near the eyelid.  The conjunctiva is made up of mucous secreting cells similar to that found in the mouth and nose and serves to help protect and lubricate the eye.

What are symptoms of conjunctivitis?
Mild cases of conjunctivitis may appear as increased tearing that is clear or colored in nature.  More severe cases can develop swollen pink or red bulging tissue that appears to almost cover the eyeball.  The eye may become increasingly painful causing a pet to hold it shut or paw/rub at eye.  In severe cases it may be difficult to see any part of the normal eye.

Why do cats and dogs develop conjunctivitis?
There are numerous reasons for the conjunctiva to become inflamed.  Infectious causes include viruses and/or bacteria.  In some cases infections will develop secondary to some other underlying cause of conjunctival inflammation.  For cats viral conjunctivitis is extremely common and closely related to upper respiratory viral infections they are exposed to at a very young age.  In several of these situations the cat may recover from the initial infection but the virus remains dormant in their body reappearing later in life at times of stress or illness.  Non-infectious causes of conjunctivitis are typically related to the anatomy (size, shape, and location) of the eyeball itself.  Dogs often develop a condition where they stop producing tears which then leads to a “dry eye” and secondary conjunctivitis.  Some breeds of cats and dogs are more prone to having flat faces or bulging eyes which can change how the eyelid sits against the eye.  In these cases eyelashes or facial fur may rub against the eye and conjunctiva causing inflammation.  Allergic disease, foreign material caught in the eye, tumors, and immune disease are all additional causes of conjunctivitis.

How is conjunctivitis diagnosed?
A veterinary examination will typically reveal the presence of conjunctivitis.  Additional testing of the cornea and tear production may also be necessary.  If systemic disease is suspected bloodwork may be recommended.  In complicated cases referral to an ophthalmologist may be recommended.

What are treatment options for conjunctivitis?
Definitive treatment of conjunctivitis involves diagnosing the underlying cause for treatment and controlling secondary bacterial infections.  This may involve topical drops or ointment, oral medications, eye lubricants, or surgery.  It is important to protect the eye from self-trauma by using a protective collar or Elizabethean collar.  Pain medication may also be prescribed to help with associated discomfort.

What is the prognosis with conjunctivitis?
Prognosis is directly related to the ability to treat the underlying condition causing the inflammation.